The present invention relates to an improved rotary looper for lockstitch sewing machines in which either a coreless thread package or a bobbin wound with thread can be received.
A conventional rotary looper comprises: a looper body which is mounted on a looper shaft, having a looper tip which grips the needle thread loop, and an inner guide which is arranged concentrically to the looper shaft; a lower bobbin-housing part which has an outer guide rib and defines a hollow for receiving the thread supply; and an upper bobbin-housing part which is equipped with a centrally arranged thread guide hole, receives the looper thread supply, is mounted in the lower bobbin-housing part, and is held in form-locked manner in the lower bobbin-housing part by at least one radially displaceable blocking member.
One prior rotary looper is known from German Patent 832,839. In accordance therewith it is possible for the looper to receive either a coreless thread package, known from German Patent 1,093,182, or a traditional bobbin wound with thread The upper bobbin-housing part of the known looper is provided at its end with an adjustable tensioning element. It is designed optimally to receive a coreless thread package, since the thread withdrawn from the center of the thread package need pass only one point of deflection on its path to the sewing area. When a traditional bobbin is placed in the upper bobbin-housing part, the thread is withdrawn from the outside diameter of the thread package on this bobbin, not the center, so the thread must be pulled over the two edges of a flange on the bobbin in order to then pass through the thread guide hole which is located centrally in the upper part of the bobbin housing. Thus, a disadvantage of the known looper is that the thread withdrawn from a traditional looper-thread bobbin is subjected to considerable frictional forces.
With respect to the largest possible supply of looper thread which is obtainable with the invention, it is known per se from the prior art (German Patent 409,711) to arrange the upper part of the bobbin housing eccentrically to the looper-shaft in the lower part of the bobbin housing, and to lengthen the upper part of the bobbin housing axially.